The portable electronic products or other electronic information products, such as the personal notebook or personal digital assistant, become indispensable electronic products in daily life. Since these electronic products are carried with the user usually, the adapter, power supply and charger are necessary accessories to keep enough power of the electronic products.
Take the adapter as an example. When the adapter is under operation, partial electric power will be consumed. With the technical progress of the electronic product and in response to the requirement of the user, more and more electronic components are loaded on the printed circuit board in the interior of the electronic product, which increases the integration of the electronic components. Therefore, the electric power consumption for the operation of most adapters is increased to 100 to 200 watts, or more than 200 watts. As the watt consumption increases, more and more heat is generated, resulting in the increase of the temperature of the whole adapter.
Please refer to FIG. 1, which is a cross-sectional view showing the structure of the conventional adapter. The adapter 1 comprises a printed circuit board (PCB) assembly 11 and a housing 12. The PCB assembly 11 comprises a printed circuit board (PCB) 13 and a plurality of electronic components 14, and is covered by a metal cover 15. When the adapter 1 is connected between the electronic product and the commercial power source and under operation, the heat generated from the electronic components 14 in the PCB assembly 11 is conducted all around, so the metal cover 15 can conduct the heat to the housing 12 to be dissipated.
The housing 12 of the adapter 1 is composed of upper and lower housings 121 and 122. Since a draft angle φ is formed to facilitate drafting during the plastic demolding process as manufacturing the upper and lower housings 121 and 122, a concave surface is formed on the inner side surface of the housing 12 after the upper and lower housings 121 and 122 are assembled, which results in that the inner side surface of the housing 12 and the vertical side surface of the PCB assembly 11 cannot conform to and stay close to each other and a space 16 is formed therebetween.
When the heat is generated from the electronic components 14, the heat flow will be toward to the area having lower thermal resistance. Since the space 16 is formed between the inner side surface of the housing 12 and the vertical side surface of the PCB assembly 11 and the thermal conductivity of the air filled in the space 16 is much lower than that of the metal cover 15 close to the top of the housing 12, the thermal resistance at the side areas of the housing 12 is higher than that at the top area of the housing 12. Therefore, the heat flow flows to the top area of the housing 12 in a major proportion, and thus, the temperature at the top surface is higher than those at the side surfaces of the adapter 1. Further, the formation of the space 16 will decrease the heat-dissipation efficiency.
Ununiform temperature distribution of the adapter 1 will cause the over-temperature of the high-temperatured heat flow area. When the high-temperatured heat flow area is close to the important electronic components on the printed circuit board, the adapter 1 will be broken easily or its lifespan will be shortened due to the over-temperature condition, and even more, a fire accident may occur. Therefore, it is needed to provide an electronic device with a heat-dissipation structure to overcome the above defects of the prior art.